Preparation and characterization of cerium-gadolinium monazites as ceramics for the conditioning of minor actinides

•The optimized condition for synthesis of Gd0.4Ce0.6PO4 solid solution is investigated.•Xenotime (GdPO4) to monazite transition occurs during the immobilization of Ce element.•Monazite-type Gd1-xCexPO4 solid solutions form in the range 0.1 ≤ x ≤ 1.•Monazite could be considered as a plausible host for minor actinide americium.

Monazites are of considerable interest for immobilization of minor actinides. In this work, the Gd1-xCexPO4 (0 ≤ x ≤ 1) series is synthesized via conventional solid–state reaction using Ce as the surrogate for minor actinide americium (Am), with microstructure/phase structure characterized by XRD, HRTEM, μ-Raman, and SEM as well. The optimized temperature for preparation of monazite-type Gd0.4Ce0.6PO4 solid solution is more than 1300 °C. At 1400 °C, the GdPO4 ceramic is essentially monazite with little metastable xenotime phase. The metastable xenotime (GdPO4) to monazite transformation occurs during the immobilizing phase of Ce element. The formation of monazite-type Gd1-xCexPO4 solid solutions in the range 0.1 ≤ x ≤ 1 is confirmed by the Rietveld refinement and Raman spectra. The change of Ce content has no significant influence on the morphology of the monazite-type Gd1-xCexPO4 compounds.